This study is designed to clinically evaluate a new non-invasive method to measure significant volume losses in surgical patients. Animal experimentation has demonstrated that the dual photon absorptiometric technique accurately measures negative and positive fluid states following hemorrhage and volume replacement. The specific research objectives are to define the accuracy of the dual photon scanner in evaluating volume shifts in operative patients, comparing this technique to clinically employed methods of volume measurement such as blood volume, I & O, serial weights, and vital signs, and to establish clinical utilization of the scan technique in monitoring and regulating fluid balance in critically ill patients. During the initial year of the research project, one hundred patients with various losses secondary to surgery will be studied. It is anticipated that this new non-invasive volume measurement technique will provide clinicians treating patients with multi-system failure with a highly accurate assessment of daily fluid balance.